Glaucoma is one of the leading causes of blindness in the United States and other industrialized countries. In fact, glaucoma is now recognized to be the number one cause of blindness in African Americans. Elevated intraocular pressure (IOP) is the key risk factor for the development of open-angle glaucoma. There is no consensus on whether early treatment of elevated IOP prevents or delays the onset of open-angle glaucoma. The proposed study is a long-term, randomized, multicenter clinical trial to determine whether medical reduction of intraocular pressure prevents or delays the onset of glaucomatous optic nerve and/or visual field damage in ocular hypertensive subjects. 1,500 subjects with IOP's greater than or equal to 24 mm Hg in at least one eye (IOP's greater than or equal to 21 mm Hg in the fellow eye) and normal visual fields and optic discs in both eyes will be assigned randomly to receive stepped medical treatment to both eyes or no treatment to both eyes. The subjects will be followed for a minimum of 5 years with automated, threshold, central, static perimetry (Humphrey program 30-2) twice a year and stereoscopic optic disc photographs once a year. The study endpoints are progressive optic disc cupping and/or reproducible glaucomatous visual field loss in either eye of a patient. All visual fields and optic disc photographs will be read in masked fashion in Reading Centers. While this trial is designed to study the efficacy and safety of early medical treatment in ocular hypertension, there will be other benefits as well. This study will allow us to refine and validate estimates of risk for individual ocular hypertensive patients in a large national sample. Furthermore, this study will also determine the conversion rate of African American ocular hypertensive subjects to open-angle glaucoma. At the conclusion of this study, practitioners should be able to make reasonable estimates of risk for individual ocular hypertensive patients and determine which ocular hypertensive individuals are most likely to benefit from early prophylactic medical treatment. The proposal describes the procedures of the Data Coordinating Center for overseeing the conduct of the study, including protocol adherence, data collection, storage and analysis.